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Old 19th March 2017, 08:28 PM   #1
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Default Tube amp with no power switch

Hi all,

This is my first post, glad to be here! Wondering if DIY audio members can help me with a question about power switches on SE tube amps. The power switch on my 8 watt, tube rectified EL34 amp just broke, and instead of replacing it, I'm thinking of just getting rid of it altogether (so that on/off is just controlled by plugging in and unplugging the amp). I am in the practice of unplugging the amp every time I turn it off anyway, so it's not going to be any inconvenience.

My question is: Would I run a risk of damage to the amp and/or tubes by controlling the on/off via just plugging in and unplugging the amp? I'm pretty sure there was a current rush to the transformers and tubes anyway when I would control this with the on/off switch (as evidenced by a brief hum when the switch was flicked on). I know sometimes when I plug things in to the wall there is a slight blue flash on the plug prongs--might this indicate current that would harm the amp?

Many thanks in advance!
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Old 19th March 2017, 09:09 PM   #2
rayma is online now rayma  United States
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Quote:
Originally Posted by Japan IV View Post
when I plug things in to the wall there is a slight blue flash on the plug prongs--
might this indicate current that would harm the amp?
Should be ok if done quickly and deliberately, or use a switched outlet strip.
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Old 19th March 2017, 09:27 PM   #3
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Quote:
Originally Posted by Japan IV View Post
Hi all,

This is my first post, glad to be here! Wondering if DIY audio members can help me with a question about power switches on SE tube amps. The power switch on my 8 watt, tube rectified EL34 amp just broke, and instead of replacing it, I'm thinking of just getting rid of it altogether (so that on/off is just controlled by plugging in and unplugging the amp). I am in the practice of unplugging the amp every time I turn it off anyway, so it's not going to be any inconvenience.

My question is: Would I run a risk of damage to the amp and/or tubes by controlling the on/off via just plugging in and unplugging the amp? I'm pretty sure there was a current rush to the transformers and tubes anyway when I would control this with the on/off switch (as evidenced by a brief hum when the switch was flicked on). I know sometimes when I plug things in to the wall there is a slight blue flash on the plug prongs--might this indicate current that would harm the amp?

Many thanks in advance!
I could not recommend operate without power switch, even also I unplug my audio equip and PC from the wall to avoid lightning.
Do your amp have soft start to slow heating the tubes or have tube rectifier?
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Last edited by FullRangeMan; 19th March 2017 at 09:31 PM.
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Old 19th March 2017, 09:30 PM   #4
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The correct in tube amps is have 2 power on switches:
First to heating the filameny,
Second to grid and HV plate,
Both must have separate softstart circuit to not stress the cold tube elements.
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Last edited by FullRangeMan; 19th March 2017 at 09:32 PM.
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Old 19th March 2017, 09:45 PM   #5
rayma is online now rayma  United States
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Originally Posted by FullRangeMan View Post
The correct in tube amps is have 2 power on switches:Both must have separate softstart
circuit to not stress the cold tube elements.
This is not necessary in tube amps using the 5AR4/GZ34 rectifier tube, which has a slow warmup filament.
For an example, the Dynaco Stereo 70, which is extremely reliable.
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Old 19th March 2017, 09:50 PM   #6
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Quote:
Originally Posted by Japan IV View Post
Hi all,

This is my first post, glad to be here! Wondering if DIY audio members can help me with a question about power switches on SE tube amps. The power switch on my 8 watt, tube rectified EL34 amp just broke, and instead of replacing it, I'm thinking of just getting rid of it altogether (so that on/off is just controlled by plugging in and unplugging the amp). I am in the practice of unplugging the amp every time I turn it off anyway, so it's not going to be any inconvenience.

My question is: Would I run a risk of damage to the amp and/or tubes by controlling the on/off via just plugging in and unplugging the amp? I'm pretty sure there was a current rush to the transformers and tubes anyway when I would control this with the on/off switch (as evidenced by a brief hum when the switch was flicked on). I know sometimes when I plug things in to the wall there is a slight blue flash on the plug prongs--might this indicate current that would harm the amp?

Many thanks in advance!
Yes, you could ha a problem by unplugging.
Reason is that plugging in or out is a inprecise action that often bounces , this
intermittent on-off-on or off-on-off can make tubes flashover.

I would recommend a mains switch, switching both leads and proper fuses.
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Old 19th March 2017, 10:57 PM   #7
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Quote:
Originally Posted by rayma View Post
This is not necessary in tube amps using the 5AR4/GZ34 rectifier tube, which has a slow warmup filament.
For an example, the Dynaco Stereo 70, which is extremely reliable.
The Dyn70 can be a reliable amp but the tubes from a late friend used to lasts only around 6 months at an point he tired to buy tubes and sold the amp.
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Old 19th March 2017, 11:25 PM   #8
rayma is online now rayma  United States
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Quote:
Originally Posted by FullRangeMan View Post
The Dyn70 can be a reliable amp but the tubes from a late friend used to lasts only around 6 months
at an point he tired to buy tubes and sold the amp.
I built, modified, and sold hundreds of Dyna Stereo 70s, and they have been extremely reliable.
If an output tube cannot last for years in this amp in normal use, it must be a poorly manufactured tube.
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Old 19th March 2017, 11:33 PM   #9
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Thanks everyone for all the replies. The amp has a 5Z4P (5V4G) rectifier--I'm not sure if this is similar to the 5AR4/GZ34 rectifier mentioned by rayma that has a slow warmup filament. Thanks also to rayma for the idea of using a switched outlet strip--I can't imagine that this would introduce much more of a current spike than the basic SPST power switch that was on the amp. So, I think I'm gonna try just joining the leads that were on the power switch and running the amp without a chassis power switch, but on a switched outlet strip. I'll try to report back on how this works out once I get the strip. Thanks again everyone and any other input is very welcome
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Old 19th March 2017, 11:53 PM   #10
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You can get arcing if the plug is pulled out slowly. This could damage your amplifier.
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